This study will determine what growth factors are involved in promoting and inhibiting mastocytosis-an abnormal increase of mast cells in one or more organ systems. Mast cells release chemicals that can cause itching, blisters, flushing, bone pain, and abdominal pain. Little is known about the disease and there is no cure. Steroids and antihistamines can help reduce some symptoms.

Patients from birth to 80 years of age with increased mast cells in at least one organ system may be eligible for this 3-year study. Family members may also be enrolled for genetic testing.

Patients will be evaluated yearly at the NIH Clinical Center with the following tests and procedures:

• Medical history and physical examination.
• Blood samples.
• Laboratory blood tests, as medically indicated.
• Bone marrow aspiration and biopsy - For the bone marrow aspiration and biopsy, the back hipbone is punctured with a sterile needle. Five milliliters (1 teaspoon) of marrow is withdrawn through a syringe and a 1/2-inch piece of tissue is extracted with a special needle.

The blood and bone marrow samples will be used for clinical care and for research to determine if mastocytosis is due to mast cell growth factors or genetic changes.

Patients who require further evaluation and tests will have recommendations made to their primary physician. Any patient who requires immediate treatment will be admitted to the hospital. Standard medical treatment may include antihistamines for itching; steroids for severe abdominal symptoms such as cramping, diarrhea, and evidence of increased mast cells determined by an upper GI study; and adrenaline for anaphylactic shock. Patients who do not respond to conventional treatment may be offered participation in an experimental therapy study.

Participating family members will have a medical history and a blood sample drawn to look for genetic abnormalities.